Sustainable Synthesis of NiMo Alloy Nanoparticles for Hydrogen Evolution Catalysis Using a Recyclable Ionic Liquid...

Advancing the sustainability of nanoparticle electrocatalyst synthesis requires reducing solvent waste without compromising catalytic performance. Here, we report a rapid, microwave-assisted colloidal synthesis of NiMo alloy nanoparticles in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-NTf₂), which serves as both reaction medium and recyclable solvent. NiMo nanoparticles with tunable compositions were obtained within 1 min at 230°C, with Ni_0.86Mo_0.14 giving the highest activity toward the hydrogen evolution reaction (HER), achieving an onset potential of -129 mV, an overpotential at 10 mA cm^-2 of -290 mV versus RHE in acidic electrolyte, and >99% Faradaic efficiency. The ionic liquid was recovered and purified via aqueous NH₄OH extraction, removing over 99% of residual Mo species, and reused for up to five successive syntheses. Nanoparticles prepared in recycled BMIM-NTf₂ retained comparable crystallinity, morphology, and catalytic activity, with stable HER performance over 45 h of electrolysis. These results demonstrate that ionic liquid recycling can improve the sustainability of the preparation of NiMo nanoparticle electrocatalysts while preserving performance and material integrity.